The HOMO-LUMO Gap as Discriminator of Biotic from Abiotic Chemistries

Low-molecular-mass organic chemicals are widely discussed as potential indicators of life in extraterrestrial habitats. However, demarcation lines between biotic chemicals and abiotic chemicals have been difficult to define. Here, we have analyzed the potential utility of the quantum chemical proper...

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Bibliographic Details
Published in:Life (Basel, Switzerland) Switzerland), 2024-10, Vol.14 (10), p.1330
Main Authors: Abrosimov, Roman, Moosmann, Bernd
Format: Article
Language:English
Subjects:
abiogenesis
Amino acids
Analysis
Bases (nucleic acids)
biosignature
Brief Report
Chemical properties
Chemical reactions
Chemicals
Extraterrestrial life
frontier orbital
Genetic code
Hydrophilicity
Indicators
life detection
Life on other planets
Metabolism
Metabolites
Meteorites
Meteors & meteorites
Microorganisms
molecular evolution
Molecular orbitals
Organic chemicals
Organic chemistry
Plant metabolites
Polymers
Quantum chemistry
Secondary metabolites
Software
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Summary:Low-molecular-mass organic chemicals are widely discussed as potential indicators of life in extraterrestrial habitats. However, demarcation lines between biotic chemicals and abiotic chemicals have been difficult to define. Here, we have analyzed the potential utility of the quantum chemical property, HOMO-LUMO gap (HLG), as a novel proxy variable of life, since a significant trend towards incrementally smaller HLGs has been described in the genetically encoded amino acids. The HLG is a zeroth-order predictor of chemical reactivity. Comparing a set of 134 abiotic organic molecules recovered from meteorites, with 570 microbial and plant secondary metabolites thought to be exclusively biotic, we found that the average HLG of biotic molecules was significantly narrower (-10.4 ± 0.9 eV versus -12.4 ± 1.6 eV), with an effect size of g = 1.87. Limitation to hydrophilic molecules (XlogP < 2) improved the separation of biotic from abiotic compounds (g = 2.52). The "hydrophilic reactivity" quadrant defined by |HLG| < 11.25 eV and XlogP < 2 was populated exclusively by 183 biotic compounds and 6 abiotic compounds, 5 of which were nucleobases. We conclude that hydrophilic molecules with small HLGs represent valuable indicators of biotic activity, and we discuss the evolutionary plausibility of this inference.
ISSN:2075-1729
2075-1729
DOI:10.3390/life14101330